Process for alkylating thiophenols in the para position with a tertiary alcohol or mercaptan



United States Patent PROCESS FOR ALKYLATIN G THIOPHENOLS IN THE PARAPOSITION WITH A TERTIARY ALCO- HOL 0R MERCAPTAN Kenneth L. Kreuz,Fishkill, N. Y., assignor to The Texas Company, New York, N. Y., acorporation of Delaware No Drawing. Application March 2, 1953, SerialNo. 339,901

7 Claims. (Cl. 260-609) This invention relates to a process forpreparing alkyl thiophenols. More particularly, it involves a processwhereby para-t-alkyl thiophenols are prepared by an alkylationprocedure.

In contrast with phenolic compounds, which are simply alkylated toproduce alkyl phenols, previous eiforts to alkylate thiophenols haveresulted in alkylation exclusively of the sulfur atom with the resultingproduction of aryl alkyl sulfides. Since efforts to effect carbonalkylation of thiophenols in the past have resulted in the production ofaryl alkyl sulfides, it has been necessary to resort to means such aszinc dust reduction of alkyl benzene sul fonyl chlorides, the reactionof diazotized alkaryl amines with hydrogen sulfide, catalytichydrogenation of aryl sulfonic acids and the action of sulfur onGrignard reagents in order to produce alkyl-substituted thiophenols. Inaddition to the tendency towards thioether formation, attemptedalkylation of thiophenols has also been complicated by the fact thatcommon alkylating catalysts such as anhydrous aluminum chloride andconcentrated sulfuric acids have tended to cause desulfurization andcondensed ring formation at relatively mild operating conditions.

This invention involves the discovery that para-t-alkyl thiophenols areproduced in substantial yield by alkylation of thiophenol and itshomologs with a particular alkylating agent at prescribed conditions.This invention provides the first means of producing alkyl thiophenolsby an alkylation process which is adaptable to commercial exploitation.

In accordance with the process of the invention,para-taliphatic-substituted thiophenols are prepared by reactingthiophenol or one of its homologs containing a hydrogen atom inpara-position with a tertiary aliphatic alcohol or mercaptan containing4 to 16 carbon atoms in the presence of an aluminum halide catalyst.Para-t-aliphaticsubstituted thiophenols include para-t-alkyl thiophenolsand para-t-alkenyl thiophenols. The alkylation proceess of the inventionis advantageously elfected at a temperature between 20 and 75 C. and atatmospheric pressure. Alkylation of thiophenols under the prescribedconditions results in the formation of a substantial yield of C-alkylateand in many cases the C-alkylate product is substantially larger thanthe S-alkylate, alkyl aryl sulfide.

The advantage of the process of this invention over previously employedprocedures for preparing alkyl thiophenols is that it is adaptable tocontinuous operation and to commercial development. The complexprocedures heretofore described are laboratory methods which are usefulto prepare small research quantities of alkyl thiophenols, but are notfeasible for commercial development because of their prohibitive cost.The instant process utilizing an alkylation reaction moves para-t-alkylthiophenols into the realm of low-cost commercial chemicals. Low-costalkyl thiophenols are of interest as lubricating oil additives becauseof the anti-oxidant and detergent properties of their metallic salts.

The thiophenol compounds employed in the process "ice of the inventionmust have a hydrogen substituted in paraposition to the --SH group onthe benzene nucleus. Since the process of the invention is specific tothe preparation of para-alkyl thiophenols, it is necessary that thepara-position be unsubstituted in order to obtain carbon alkylation.Examples of thiophenol homologs that may be employed in the process ofthe invention are 0- thiocresol, o-ethylthiophenol, o-butenylthiophenol,mbutylthiophenol and o-hexylthiophenol. In general, 0- and m-substitutedalkyl thiophenols in which the alkyl group contains from about 1 to 10carbon atoms are usable in the process of the invention to preparepara-t-alkyl thiophenols.

Alkylation of para-substituted thiophenols by the process of theinvention results in the introduction of an aliphatic group solely onthe sulfur atom. Reaction of parathiocresol with tertiary butyl alcoholin the presence of aluminum chloride resulted in the formation of almosttheoretical yields of the sulfur alkylation product, namely,tolyl-t-butyl sulfide. It is also significant that once an alkyl grouphas entered into the para-position, further substitution on the carbonatoms of the benzene ring by alkyl groups is not effected by thisinvention.

Aluminum chloride, aluminum bromide and aluminum iodide can be employedas catalysts to effect replacement of a hydrogen atom by a tertiaryaliphatic group in the para-position on a thiophenol compound. Aluminumchloride, of course, is the preferred reagent because of its low costand ready availability.

The alkylating agent used in this invention is a tertiary aliphaticalcohol or mercaptan containing between 4 and 16 carbon atoms; t-alkyland t-alkenyl alcohols and mercaptans of prescribed chain length areincluded Within this definition. It is preferred to use alcohols andmercaptans containing between 4 and 12 carbon atoms because separationof higher molecular Weight alkylated thiophenols from the reactionproduct is not simply effected. Tertiary aliphatic alcohols andmercaptans are by definition compounds wherein the hydroxyl group orsulfhydroxyl group is attached to a carbon atom which is attached tothree carbon atoms. Tertiary butyl alcohol, 1,1-dimethyl-1-hydroxybutene-Z (a t-hexenyl alcohol), t-butyl mercaptan, t-amyl alcohol andt-amyl mercaptan are particularly preferred alkylating agents.

The substitution of primary and secondary alcohols for tertiary alcoholsas alkylating agents results in the production of a sulfur alkylationproduct exclusively. The high specificity of the process to tertiaryalcohols and mercaptans is particularly surprising in view of the highyields of C-alkylate obtained therewith.

The preparation of para-alkyl thiophenols is effected at a temperaturebetween 20 and C. with temperatures between 35 and 65 C. beingpreferred. The temperature is maintained within the prescribed limits byeffecting the alkylation in a low boiling hydrocarbon solvent such aspetroleum ether.

The reaction is also normally effected at atmospheric pressure becausethe use of elevated pressures does not materially improve the yield ofp-alkyl thiophenol.

It has also been found that the highest yields of parat-alkyl thiophenolare obtained when the mol ratios of reactants and catalyst aremaintained within particular, well-defined limits. The use ofthiophenol, alkylating agent and catalyst in ratios between 1:121 and1:03:03 results in the production of maximum yields of C-alkylate.Outside of the prescribed mol ratios of reactants and catalyst, loweryields of C-alkylate are obtained and the S-alkylation product, an arylalkyl sulfide, is the major component of the reaction product. Use ofexcessive or minute amounts of aluminum halide catalyst causessubstantial reduction in the yield of C-alkylate; for example,

when the mol of aluminum chloride is either equivalent to or less thanone sixth of the mol sum of the thiophenol and alkylating agent, theyield of C-alkylate is very small. It has been discovered thatparticularly high yields of para-alkyl thiophenol are obtained whenthiophenol, alk ylating agent and catalyst are employed in a ratio of 3mols of thiophenol, 2 mole of alkylating agent and 1 mol ofcatalyst.

The process of the invention is similar to commercial alkylationprocesses, and is effected either batch-wise or continuously. In batchoperation, the thiophcncl con.- pound containing a hydrogen substitutedin the paraposition, the alkylating agent and a hydrocarbon solvent suchas petroleum ether are added to a reaction vessel; the aluminum halidecatalyst is added to the reaction mixture in small increments; afteraddition of all the catalyst, the mixture is refluxed or stirred withoutrefluxing for a period of the order of 1 to 5 hours at which time thereaction is substantially complete. In the event that acontinuousprocess is employed, it is recommended that the reactants be in contactwith the catalyst for a period of 30 to 60 minutes.

The process of the invention is illustrated in the following exampleswhich demonstrate that para-t-alkyl thiophenols are produced insubstantial yield by the reaction of the thiophenol compound containinga hydrogen atom in the para-position with tertiary butyl alcohol ormercaptan in accordance with the process of the invention.

Example I 93 g. (0.75 mol) of o-thiocresol, 37 g. (0.5 mol) of t-butylalcohol and 400 cc. of petroleum other were charged to a three-neckflask fitted with a stirrer and refiux condenser. 34 g. (0.25 mol) ofaluminum chloride was added to the stirred reaction mixture in smallproportions such that the heat of reaction caused gentle refluxing.After addition of the aluminum chloride was complete, the reactionmixture was stirred for a period of 2.8 hours and then allowed to standovernight at room temperature. The reaction product consisting of aclear supernatant liquid and an orange colored solid phase washydrolyzed by pouring on a mixture of ice and hydrogen chloride. Thehydrolyzed mixture was extracted with ether which was, in turn,extracted with per cent sodium hydroxide to efiect separation of theproduct into neutral and acidic fractions; the neutral fraction containsthe S-alkylate, and the acidic fraction comprises unreacted thiocresoland the C-alkylate. The caustic extract was acidified with hydrochloricacid, and the acidified mixture g 51 g. (0.41 mol) of o-thiocresol, 21.3g. (0.27 mol) of t-butyl alcohol and 200 cc. of petroleum ether werecharged to a three-neck flask, and 18.5 g. (0.14 mol) of aluminumchloride was added thereto with stirring. The reaction conditions werethose described in Example I with the exception that the reactionmixture, after all the aluminum chloride had been added thereto, washeated under reflux for one hour prior to standing overnight. From thereaction product which was worked up in accordance with the proceduredescribed in Example I, there was obtained g. ofpara-t-butyl-o-thiocresol which is a theoretical yield of 52 per centbasis the t-butyl alcohol charged. There was also obtained 15.2 g. oft-butylo-tolyl sulfide which is a yield of about 31.2 per cent basis ofthe t-butyl alcohol charged.

Example III 55 g. (0.50 mol) of thiophenol, 37 g. (0.50 mol) of t-butylalcohol and 200 cc. of petroleum ether were charged to a three-neckflask, and 68 g. (0.50 mol) of aluminum chloride was added to thismixture with stirring. The mol ratio of thiophenol, t-butyl alcohol andaluminum chloride catalyst was 1:1:1. The reaction conditions describedin Example I were followed with the exception that the reaction mixture,after addition of aluminum chloride, was heated under reflux for onehour prior to standing overnight. From the reaction. product which wasworked up in accordance with the procedure described in Example I, therewas obtained 27.4 g. of para-t-butyl thiophenol, which is a yield of 33per cent basis the t-butyl alcohol charged. There was also obtained 28g. of t-butyl phenyl sulfide which is a theoretical yield ofapproximately 33.6 per cent basis t-butyl alcohol charged.

Example I V 83 g. (0.75 mol) of thiophenol, 37 g. (0.5 mol) of t-butylalcohol and 200 cc. of petroleum ether were added to a three-neck flask;68 g. (0.5 mol) of aluminum chloride was added slowly to the stirredreaction mixture. The mol ratioof reactants and catalyst was 3:212. Thereaction conditions were those used in Example III. From the reactionproduct, which was treated in accordance with the procedure described inExample I, there was isolated 29.9 g. of para-t-butyl thiophenol whichis the theoretical yield of 36 per cent basis t-butyl alcohol charged.There was also obtained 29.2 g. of t-butyl phenyl sulfide which is ayield of approximately 35.2 per cent basis t-butyl alcohol charged.

Example V 83- g. (0.75 mol) of thiophenol, 37 g. (0.5 mol) of t-butylalcohol and 200 cc. of petroleum ether were added to a three-neck flask;34 g. (0.25 mol) of aluminum chloride was slowly added to the reactionmixture with stirring. The reaction conditions were those used inExample IV. The mol ratio of thiophenol, t-butyl alcohol and catalystwas 3:2:1. From the reaction product which was worked up in accordancewith the procedure described in Example I, there was obtained 37.7 g. ofpara-t-butyl thiophenol which is a yield of 45 per cent basis of t-butylalcohol charged. There was also obtained 32.8 g. of t-butyl phenylsulfide, which is a yield of 38 per cent basis t-butyl alcohol charged.

Example VI 50 g. (0.4 mol) of o-thiocresol, 29 g. (0.24 mol) of t-amylmercaptan and 200 cc. of petroleum ether were added to a three-neckflask; 19 g. (0.14 mol) of aluminum chloride was slowly added withstirring to the reaction mixture. The reaction conditions were similarto those employed in Example I with the exception that the reactionmixture was stirred wihout refluxing for six hours prior to standingovernight. From the reaction product which was worked up in accordancewith the procedure outlined in Example I, there was recovered 12 g. ofparat-amylmercapto-o-thiocresol, which is a yield of 25 per cent basist-amyl mercaptan charged. There was also obtained 25.8 g. oft-amyl-o-tolyl sulfide which is a yield of approximately 53.6 per centbasis the t-amyl mercaptan charged.

Example VII 104 g. (0.75 mol) of o-ethyl thiophenol, 37 g. (0.5 mol) oft-butyl alcohol and 200 cc. of petroleum ether were added to athree-neck flask; 34 g. (0.25 mol) of aluminum chloride was slowly addedwith stirring to the reaction mixture. The reaction conditions weresimilar to those employed in Example I with the exception that thereaction mixture, after addition of aluminum chloride, was heated underreflux for 1.3 hours prior to standing overnight. From the reactionproduct, which was worked up in accordance with the procedure outlinedin Example I, there was recovered 28 g. of para-t-butyl a1- coholcharged. There was also obtained 57.3 g. of t butyl-o-ethyl phenylsulfide which is a yield of approximately 59 per cent basis the t-butylalcohol charged.

Examples I and II illustrate the high yields of carbon alkylate that canbe obtained in the process of this invention at the preferred mol ratioof reactants and catalysts, namely, 3 mols of thiophenol, 2 mols oftertiary alcohol or mercaptan and 1 mol of catalyst; yields of carbonalkylate higher than 50 per cent are obtained in both of these examples.Comparison of Examples II, III and IV definitely proves that the 3:2:1mol ratio of thiophenol, tertiary alcohol and catalyst gives the optimumyields of carbon alkylate; the preferred 3:2:1 mol ratio employed inExample V gives a carbon alkylate yield of 45 per cent, whereas the12121 mol ratio employed in Example II gives a yield of 33 per centcarbon alkylate and the 322:2 mol ratio employed in Example III gives a36 per cent yield of carbon alkylate.

Example VI demonstrates the use of tertiary alkyl mercaptans in theprocess of the invention. Example VII applies the process of theinvention to higher homologs of thiophenol.

Obviously, many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof and, therefore, only such limitations should beimposed as are indicated in the appended claims.

I claim:

1. A process for preparing para-t-aliphatic-substituted thiophenolswhich comprises reacting a thiophenol containing a hydrogen atom inpara-position with an alkylating agent selected from the groupconsisting of tertiary alkyl and alkenyl alcohols and mercaptanscontaining four to sixteen carbon atoms, effecting said reaction in thepresence of a catalyst selected from the group consisting of aluminumchloride, aluminum iodide and aluminum bromide at a temperature between20 and C. so that substantial carbon alkylation in the para positionoccurs.

2. A process according to claim 1 in which aluminum chloride is employedas the catalyst.

3. A process according to claim 1 in which thiophenol, an alkylatingagent and aluminum halide catalyst are employed in a mol ratio in therange of 1:1:1 to 1:03:03.

4. A process according to claim 1 in which the process is efiected atatmospheric pressure.

5. A process according to claim 1 in which the alkylating agent containsfour to twelve carbon atoms.

6. A process according to claim 1 in which the reaction is elfected in alow boiling hydrocarbon solvent.

7. A process for preparing para-t-butyl-o-thiocresol which comprisesreacting thiocresol with t-butyl alcohol and effecting said reaction inthe presence of aluminum chloride in a petroleum ether solvent at atemperature between 20 and 75 C.

Recueil des Travaux Aux Chirniques, 69, page 644. Huston et al: 58, J.A. C. S. (1936) pages 439-441.

1. A PROCESS FOR PREPARING PARA-T-ALIPHATIC-SUBSTITUTED THIOPHENOLSWHICH COMPRISES REACTING A THIOPHENOL CONTAINING A HYDROGEN ATOM INPARA-POSITION WITH AN ALKYLATING AGNET SELECTED FROM THE GROUPCONSISTING OF TERTIARY ALKYL AND ALKENYL ALCOHOLS AND MERCAPTANSCONTAINING FOUR TO SIXTEEN CARBON ATOMS, EFFECTING SAID REACTION IN THEPRESENCE OF A CATALYST SELECTED FROM THE GROUP CONSISTING OF ALUMINUMCHLORIDE, ALUMINUM IODIDE AND ALUMINUM BROMIDE AT A TEMPERATURE BETWEEN20 AND 75* C. SO THAT SUBSTANTIAL CARBON ALKYLATION IN THE PARA POSITIONOCCURS.